In electrophotography, also known as Xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Although excellent toner images may be obtained with multilayered belt or drum photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators, and printers are developed, there is a greater demand on print quality. The delicate balance in charging image and bias potentials, and characteristics of the toner and/or developer, must be maintained. This places additional constraints on the quality of photoreceptor manufacturing, and thus on the manufacturing yield.
Imaging members are generally exposed to repetitive electrophotographic cycling, which subjects the exposed charged transport layer or alternative top layer thereof to mechanical abrasion, chemical attack and heat. This repetitive cycling leads to gradual deterioration in the mechanical and electrical characteristics of the exposed charge transport layer. Physical and mechanical damage during prolonged use, especially the formation of surface scratch defects, is among the chief reasons for the failure of belt photoreceptors. Therefore, it is desirable to improve the mechanical robustness of photoreceptors, and particularly, to increase their scratch resistance, thereby prolonging their service life. Additionally, it is desirable to increase resistance to light shock so that image ghosting, background shading, and the like is minimized in prints.
Providing a protective or wear-resistant overcoat layer is a conventional means of extending the useful life of photoreceptors.
However, in scorotron xerography, the low wear overcoats are associated with poor Lateral Charge Migration (LCM) that is due to the aggressive scorotron generated corona. A second problem is the decrease in discharge rate associated with applying a cross-linked overcoat layer on top of a traditional charge transport layer. The problem of discharge rate reduction when applying low wear cross-linked overcoat layers was due to a reduction in average charge mobility throughout the photosensitive layers. This problem was overcome by using a structured organic film (SOF) design which provides a robust surface that is low wear and scratch resistant. SOF compositions have been described in U.S. Pat. No. 8,372,566, which is incorporated by reference herein in its entirety. Such SOF compositions are chemically and mechanically robust materials that demonstrate many superior properties to conventional photoreceptor materials and increase the photoreceptor life by preventing chemical degradation pathways caused by the xerographic process.
However, the poor LCM problem remained with the SOF design and the devices remain unusable in scorotron xerography. Therefore, there exists a need to further increase the LCM performance of the SOF design to enable usage in scorotron xerography for long term printing.